As part of the development of the high speed router platform program, the GSR (Gigabit Switch Router) backplanes are required to speed up to a 5 Gbit/sec data transfer rate from the 1.25 Gbit/sec rate that the backplanes were designed for.
Dealing with such speed is very challenging and requires special techniques to deal with problems beyond just simple signal integrity. At high data transfer rates of 2.5 Gbit/sec or more, most of the noise injected into the signal is crosstalk caused at the connector.
The main noise contributor is near-end crosstalk (NEXT). The terminology of NEXT will be briefly explained with reference to FIG. 1 which depicts a transmitter (Tx) and Tx line, a Receiver (Rx) and Rx line, and a connector. In this case the transmitter is the crosstalk aggressor and the receiver is the crosstalk victim. Crosstalk is the same on all Rx channels from each aggressor. Generally, the Tx and Rx lines are interleaved on the backplane so that there are 2 aggressors for all the Rx channels except one. The channel at the end has one aggressor.
One of the only effective ways to deal with high speed connector crosstalk is with crosstalk cancelling. Today's backplane and connector technology cannot scale to the required 5 Gbit/sec rate unless sophisticated DSP based technology is used. However, DSP technology is power hungry and complex to implement.